1. Field of the Invention
The present invention deals with providing low-resistance paths between pads of a circuit to facilitate the dissipation of ESD current.
2. Background Art
Electrostatic discharge (ESD) events result in high voltage and current transients that can damage electrical devices. For example, if these transient voltages and currents are not safely discharged, they can generate heat. This generated heat can, for example, damage elements of an integrated circuit (IC). Thus, a goal of ESD protection devices is to facilitate the safe discharge ESD event transients. Further, voltage amplitudes of the transient voltages can exceed the breakdown voltage of transistor devices, which causes failure.
To prevent ESD currents from damaging circuit components, a path is provided between pads of the circuit. In such a manner, an ESD event between any two pads can be discharged. Furthermore, it is desirable that the path be low-resistance to reduce the likelihood that the ESD current will damage components as it travels between the two pads. Existing systems couple all rails and all pads associated with circuit blocks of a segment to a segment ground rail. Each segment ground rail is then coupled to a circuit-wide ground rail. Through the respective segment ground rails and the circuit-wide ground rail, then, each pad associated with the circuit is coupled to all other pads.
Some circuit designs require circuit segments to include a negative supply rail, e.g., in addition to a positive supply rail and segment ground rail. For example, I/O pads may require a negative supply rail so that they can swing from a negative voltage to a positive voltage. Existing ESD protection systems however cannot be extended to provide ESD protection to circuits including circuit segments that have negative supply rails. For example, diode connections between the negative supply rail and the segment ground rail or the circuit-wide ground rail may be forward biased during normal operation, resulting in undesired short circuits.
What is needed, then, is an ESD protection system that provides ESD protection for circuits including circuit segments that have negative supply rails.